Human Infection with Swine Influenza Virus -- Wisconsin
An influenza virus isolated from a 32-year-old Wisconsin woman
who had
been exposed to pigs has been identified as a swine influenza
virus. On
September 13, 1988, when the woman was in her 36th week of
pregnancy,
she was admitted to a community hospital with a 1-week history of
fever
to 102 F (38.9 C), headache, myalgias, 3 days of nonproductive
cough,
and 1 day of progressive shortness of breath. The patient had
radiologic evidence of pneumonitis with bilateral lower lobe
consolidation and was treated with broad-spectrum antibiotics. On
September 14, she was transferred to a tertiary-care hospital for
ventilatory assistance and management of late-stage pregnancy.
Specimens for bacterial, viral, and fungal cultures and serologic
testing were obtained, and antibiotic therapy was continued.
Because of
mechanical difficulty in ventilating the patient, labor was
induced,
and on September 17 she gave birth to a healthy 2990-g infant.
Despite intensive support, her respiratory failure persisted, and
she
died September 21.
The patient's clinical course and findings of postmortem
examinations
were consistent with primary viral pneumonia. All cultures for
bacteria
and fungi were negative. Influenza virus was isolated postmortem
from a
sputum specimen obtained on September 14 and was identified by
monoclonal antibody as type A virus. When further tested by
hemagglutination inhibition (HI) tests at CDC, the virus was
unreactive
with antisera to strains currently prevalent in the world but
reacted
with antisera to influenza A(H1N1) viruses related to swine
influenza.
A paired serum specimen showed a fourfold or greater rise in HI
antibody against swine influenza virus. Results of preliminary HI
tests
performed at the University of Wisconsin with monoclonal antibodies
to
the hemagglutinin of swine influenza virus indicate that the
isolate
resembles viruses isolated during the summer from pigs in
Wisconsin.
Further laboratory studies of the recent Wisconsin isolate are
being
undertaken to confirm its similarity to enzootic strains.
On September 3, 4 days before the onset of illness, the woman had
attended a county fair and had visited the display area of a pig
barn.
Veterinarians working at the fair stated that influenza-like
illness
had occurred among pigs at the fair.
Preliminary investigations have detected no outbreaks of
influenza-like illness in the surrounding communities. Further
investigation is under way to determine whether the swine influenza
virus may have infected others with known exposure to pigs at the
fair
or from the ill woman to persons with whom she had close contact.
Reported by: J Kaufman, MD, M Hassan, MD, M Rytel, MD, R Chayer,
MD, P
Volkert, MD, P McKinney, MD, J Michaels, C Farmer, PhD, Milwaukee
County Medical Complex; G Sedmak, Milwaukee Bureau of Laboratories,
Milwaukee; BC Easterday, DVM, VS Hinshaw, PhD, Dept of Veterinary
Medicine, Univ of Wisconsin, Madison; J Berg, D Hopfensperger, M
Proctor, PhD, JP Davis, MD, State Epidemiologist, Wisconsin Dept of
Health and Social Svcs. TF Smith, PhD, Mayo Clinic, Rochester,
Minnesota. WHO Collaborating Center for Influenza, Influenza Br,
and
Epidemiology Office, Div of Viral Diseases, Center for Infectious
Diseases, CDC.
Editorial Note
Editorial Note: Influenza A viruses circulate naturally in many
nonhuman hosts including swine, horses, and numerous avian species
(1).
Such viruses are theoretically reservoirs from which strains
capable of
infecting humans may evolve; however, the genetic composition of
most
animal influenza viruses appears to biologically restrict the range
of
hosts and prevent the viruses from crossing the species barrier. In
some cases, however, this barrier appears to have been
circumvented.
For example, "Hong Kong flu" emerged in 1968 by probable genetic
reassortment between the previously circulating human strains of
"Asian
flu" and an animal virus that donated the gene for the new virus
hemagglutinin (2).
Unlike the 1968 event, the case in Wisconsin probably represents
direct transmission of influenza virus from a pig to a human host.
Virus isolation on other occasions has proven that viruses
genetically
similar to those found in swine in the United States have caused
human
infections. The first proven case was in 1974 and involved a child
with
Hodgkin's disease who had known contact with pigs (3). Since then,
other laboratory-confirmed cases have occurred in persons who
either
resided on farms or visited locations where contact with pigs was
possible (4). Infections also have occurred without demonstrated
exposure to swine, including the 1976 cluster of cases in Fort Dix,
New
Jersey, which showed limited person-to-person transmission (5), and
possibly a case in a child in Las Vegas (6). In these situations,
initial undocumented transmission of influenza virus from swine to
humans is likely to have occurred, and the infected person probably
initiated limited chains of person-to-person transmission (possibly
with
subclinical infections), which eventually led to the laboratory-
diagnosed cases. In addition to the recent Wisconsin case, other
human
infections with swine influenza viruses have been fatal (4). The
fatalities have occurred in human hosts who were immunosuppressed
or
otherwise compromised by stressful occupational or medical
conditions.
However, continuous transmission of swine influenza virus in humans
has
not occurred.
References
Kilbourne ED. Influenza. New York: Plenum Medical Book,
1987.
Palese P, Kingsbury DW, eds. Genetics of influenza viruses.
New
York: Springer-Verlag/Wien, 1983.
Smith TF, Burgert EO Jr, Dowdle WR, Noble GR, Campbell RJ, Van
Scoy
RE. Isolation of swine influenza virus from autopsy lung
tissue
of man. N Engl J Med 1976;294:708-10.
Hodder RA, Gaydos JC, Allen RG, Top FH Jr, Nowosiwsky T,
Russell
PK. Swine Influenza A at Fort Dix, New Jersey
(January-February
1976). III. Extent and spread and duration of the outbreak. J
Infect Dis 1977;136(suppl):S369-75.
Patriarca PA, Kendal AP, Zakowski PC, et al. Lack of
significant
person-to-person spread of swine influenza-like virus
following
fatal infection in an immunocompromised child. Am J Epidemiol
1984;119:152-8.
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